U.S. patent application number 13/178667 was filed with the patent office on 2012-01-12 for compression of direct methanol fuel cell stacks with catalyst coated membranes and membrane electrode assembly.
This patent application is currently assigned to OORJA PROTONICS INC.. Invention is credited to Paul Knauer, Derek Kwok, Bhaskar Sompalli.
Application Number | 20120009493 13/178667 |
Document ID | / |
Family ID | 45438828 |
Filed Date | 2012-01-12 |
United States Patent
Application |
20120009493 |
Kind Code |
A1 |
Sompalli; Bhaskar ; et
al. |
January 12, 2012 |
COMPRESSION OF DIRECT METHANOL FUEL CELL STACKS WITH CATALYST
COATED MEMBRANES AND MEMBRANE ELECTRODE ASSEMBLY
Abstract
An apparatus to control a swelling of a catalyst coated membrane
in a fuel cell includes an insulator layer provided at a perimeter
of the fuel cell. The insulator layer has a plurality of insulator
films and is secured to a flow field plate. The insulator layer has
a less compressibility relative to a gasket used in the fuel cell.
A method for controlling a swelling of a catalyst coated membrane
in a fuel cell includes providing an insulator layer at a perimeter
of each of fuel cells in a fuel cell stack. The fuel cell stack is
compressed for a predetermined duration when the catalyst coated
membrane is in a substantially dry state. Passage of fuel is
allowed inside the fuel cell thereby facilitating the catalyst
coated membrane to swell. A swollen catalyst coated membrane is
allowed to contact the insulator layer.
Inventors: |
Sompalli; Bhaskar; (Fremont,
CA) ; Knauer; Paul; (Fremont, CA) ; Kwok;
Derek; (Fremont, CA) |
Assignee: |
OORJA PROTONICS INC.
Fremont
CA
|
Family ID: |
45438828 |
Appl. No.: |
13/178667 |
Filed: |
July 8, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61363048 |
Jul 9, 2010 |
|
|
|
Current U.S.
Class: |
429/429 ;
429/480; 429/508 |
Current CPC
Class: |
Y02E 60/523 20130101;
H01M 8/241 20130101; H01M 8/248 20130101; H01M 8/1011 20130101;
Y02E 60/50 20130101; H01M 8/0276 20130101; H01M 8/0258
20130101 |
Class at
Publication: |
429/429 ;
429/508; 429/480 |
International
Class: |
H01M 8/04 20060101
H01M008/04; H01M 8/10 20060101 H01M008/10; H01M 2/08 20060101
H01M002/08 |
Claims
1. An apparatus to control a swelling of a catalyst coated membrane
in a fuel cell, said apparatus comprising: an insulator layer
provided at a perimeter of the fuel cell.
2. The apparatus as claimed in claim 1, wherein said insulator
layer comprises a plurality of insulator films.
3. The apparatus as claimed in claim 1, wherein said insulator
layer has a less compressibility relative to a gasket used in the
fuel cell.
4. The apparatus as claimed in claim 3, wherein said insulator
layer defines an opening to receive the gasket therein.
5. The apparatus as claimed in claim 4, wherein said insulator
layer is secured to at least one flow field plate.
6. A method for controlling a swelling of a catalyst coated
membrane in a fuel cell, said method comprising: providing an
insulator layer at a perimeter of each of fuel cells in a fuel cell
stack; compressing said fuel cell stack for a predetermined
duration when said catalyst coated membrane is in a substantially
dry state; allowing passage of fuel inside the fuel cell thereby
facilitating said catalyst coated membrane to swell; and allowing
said swollen catalyst coated membrane to contact said insulator
layer thereby preventing further swelling of said catalyst coated
membrane.
7. The method as claimed in claim 6, wherein allowing said swollen
catalyst coated membrane to contact said insulator layer includes
allowing a gas diffusion layer to contact a plurality of ribs
provided on a respective flow field plate.
8. The method as claimed in claim 6 further comprising, compressing
said fuel cell stack after allowing said swollen catalyst coated
membrane to contact said insulator layer.
9. The method as claimed in claim 6, wherein the insulator layer
includes a plurality of insulator films.
10. A fuel cell comprising: a catalyst coated membrane; and an
apparatus to control swelling of said catalyst coated membrane,
wherein said apparatus comprises an insulator layer provided at a
perimeter of said fuel cell.
11. The apparatus as claimed in claim 10, wherein said insulator
layer comprises a plurality of insulator films.
12. The apparatus as claimed in claim 10, wherein said insulator
layer has a less compressibility relative to a gasket used in the
fuel cell.
13. The apparatus as claimed in claim 12, wherein said insulator
layer defines an opening to receive the gasket therein.
14. The apparatus as claimed in claim 13, wherein said insulator
layer is secured to at least one flow field plate.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from U.S. Provisional
Application No. 61/363,048, filed on Jul. 9, 2010, the complete
disclosure of which is incorporated fully herein by reference.
TECHNICAL FIELD
[0002] The embodiments herein generally relate to fuel cell stacks,
and, more particularly, but not exclusively, to fuel cells
employing an apparatus and a method for controlling swelling of a
catalyst coated membrane and a MEA.
BACKGROUND
[0003] A fuel cell, like an ordinary battery, provides direct
current electricity from two electrochemical reactions. The
electrochemical reactions occur at electrodes to which reactants
are fed. A fuel cell stack typically includes a series of
individual fuel cells. Each cell includes an anode and a cathode. A
voltage across each cell is determined by the type of
electrochemical reaction occurring in the cell. For example, for a
typical direct methanol fuel cell (DMFC), the voltage can vary from
0.2 V to 0.9 V, depending on a current being generated. The current
being generated in the cell depends on the operating condition and
design of the cell, such as electro-catalyst composition or
distribution and active surface area of a membrane electrode
assembly (MEA), characteristics of a gas diffusion layer (GDL),
anode and cathode flow field designs, cell temperature, reactant
concentration, reactant flow and pressure distribution, reaction
by-product removal, and so forth. A reaction area of a cell, number
of cells in series, and the type of electrochemical reaction in the
fuel cell stack determine the current and hence the power supplied
by the fuel cell stack. For example, typical power for a direct
methanol fuel cell (DMFC) stack can range from a few watts to a few
kilowatts. A fuel cell system typically integrates a fuel cell
stack with different subsystems for the management of water, fuel,
air, humidification, and thermal condition. These subsystems are
sometimes collectively referred to as balance of the plant
(BOP).
[0004] FIG. 1, illustrates a typical direct methanol fuel cell 10
(DMFC). As illustrated in FIG. 1, the direct methanol fuel cell 10
(DMFC) has a negative electrode 12a (anode), a positive electrode
12c (cathode), a catalyst coated membrane 12m, an anode flow field
plate 13a and a cathode flow field plate 13b. The anode 12a is
maintained by supplying a fuel such as a liquid methanolic solution
(e.g., having a concentration in the range of 0.5 M to 5 M) and the
cathode 12c is maintained by supplying oxygen or air. When
providing a current, methanol is electrochemically oxidized at an
anode electro-catalyst to produce electrons. The electrons travel
through an external circuit (not shown) to a cathode
electro-catalyst where the electrons are consumed together with
oxygen in a reduction reaction. A circuit is maintained within the
direct methanol fuel cell 10 (DMFC) by the conduction of protons in
the catalyst coated membrane 12m. The catalyst coated membrane 12m
is typically formed of a perfluorosulfonic acid (PFSA)-based
material, such as a material sold under the trademark Nafion.RTM..
The catalyst coated membrane 12m is proton-conducting and typically
requires humidification to operate efficiently. The effectiveness
of the catalyst coated membrane 12m depends on gas diffusion layers
G which are in communication with the catalyst coated membrane 12m
for electronic contact and for aiding mass transport of reactants
and by-products. The gas diffusion layer G allows access to
methanolic solution and remove carbon dioxide CO2 gas formed at the
anode 12a side. At the cathode 12c side, the gas diffusion layer G
allows access to air and remove water. The catalyst coated membrane
12m and the gas diffusion layers G operate efficiently when mass
transport of reactants and by-products occurs smoothly. The
effectiveness of the mass transport is typically affected by the
degree of compression of the gas diffusion layers G, and other
characteristics such as porosity and Teflon content. A certain
degree of compression is desirable to reduce Ohmic resistances
between the anode flow field plate 13a and the cathode flow field
plate 13b, the gas diffusion layers G, and the catalyst coated
membrane 12m. However, too high a compression can crush fibers
forming the gas diffusion layers G and close pores through which
mass transport occurs which may result in damage of the
electrodes.
[0005] Further, when the catalyst coated membrane 12m formed of a
PFSA-based material is included within the cell 10, the catalyst
coated membrane 12m is typically compressed in a dry form along
with the gas diffusion layers G and an elastomeric, compressible
gasket 14, as illustrated in FIG. 2. The catalyst coated membrane
12m tends to swell from about 50% to about 120% (e.g., by volume),
when subsequently contacted with a solvent-based fuel, such as a
methanolic solution in conjunction with a higher temperature. Due
to the presence of the gasket 14, membrane swell along the x-y
directions (e.g., along a plane facing the flow field plate) is
substantially impeded by the gasket 14. However, the catalyst
coated membrane 12m will be free to swell along z-direction (e.g.,
vertically in FIG. 2) into any remaining free volume. Because of
the compression of the gasket 14, the remaining free volume to
accommodate membrane swell can be substantially localized in
channel areas C, as illustrated in FIG. 3. For the direct methanol
fuel cell 10 (DMFC) where a need for accommodation of the evolved
CO2 and low pressure drops can lead to deep and wide anode
channels, the free volume available for membrane swell can be
relatively high (e.g., up to 500 ml in some stacks). In such case,
membrane swell can cause undesirably high compressive forces to
develop in the channel areas. These high compressive forces, in
turn, can lead to over-compression of the gas diffusion layers G,
thus leading to undesirable mass transport restrictions and
potentially damage at the anode 12a side. A similar situation could
develop on the cathode 12c.
[0006] Therefore, there is a need to develop fuel cells employing
an apparatus and a method for controlling swelling of a catalyst
coated membrane.
SUMMARY
[0007] In view of the foregoing, an embodiment herein provides an
apparatus to control a swelling of a catalyst coated membrane in a
fuel cell. The apparatus includes an insulator layer provided at a
perimeter of the fuel cell. The insulator layer has a plurality of
insulator films and is secured to a flow field plate. The insulator
layer has a less compressibility relative to a gasket used in the
fuel cell.
[0008] Embodiments further disclose a method for controlling a
swelling of a catalyst coated membrane in a fuel cell includes
providing an insulator layer at a perimeter of each of fuel cells
in a fuel cell stack. The fuel cell stack is compressed for a
predetermined duration when the catalyst coated membrane is in a
substantially dry state. The method further includes allowing
passage of fuel inside the fuel cell thereby facilitating the
catalyst coated membrane to swell. The method also includes
allowing swollen catalyst coated membrane to contact the insulator
layer thereby preventing further swelling of said catalyst coated
membrane.
[0009] These and other aspects of the embodiments herein will be
better appreciated and understood when considered in conjunction
with the following description and the accompanying drawings.
BRIEF DESCRIPTION OF THE FIGURES
[0010] The embodiments herein will be better understood from the
following detailed description with reference to the drawings, in
which:
[0011] FIGS. 1-3 illustrate a typical direct methanol fuel
cell;
[0012] FIG. 4 illustrates a portion of a fuel cell according to an
embodiment of the invention; and
[0013] FIG. 5 is a perspective view of the fuel cell of FIG. 4
according to an embodiment.
DETAILED DESCRIPTION OF EMBODIMENTS
[0014] The embodiments herein and the various features and
advantageous details thereof are explained more fully with
reference to the non-limiting embodiments that are illustrated in
the accompanying drawings and detailed in the following
description. Descriptions of well-known components and processing
techniques are omitted so as to not unnecessarily obscure the
embodiments herein. The examples used herein are intended merely to
facilitate an understanding of ways in which the embodiments herein
may be practiced and to further enable those of skill in the art to
practice the embodiments herein. Accordingly, the examples should
not be construed as limiting the scope of the embodiments
herein.
[0015] The embodiments herein disclose an apparatus and a method
for controlling swelling of a catalyst coated membrane in a fuel
cell. Referring now to the drawings, and more particularly to FIGS.
4 and 5, where similar reference characters denote corresponding
features consistently throughout the figures, there are shown
embodiments.
[0016] FIG. 4 illustrates a portion of a fuel cell 10 according to
an embodiment of the invention. The fuel cell 10 according to FIG.
4 has an insulator layer 40 configured to be located at a perimeter
of the fuel cell 10. The insulator layer 40 can be formed of any
appropriate insulator material. The insulator layer 40 may be
secured to the flow field plate 13a of the fuel cell 10 by any
securing means known in the art. Further, the insulator layer 40
defines an opening O surrounding a compressible, elastomeric gasket
14. The insulator layer 40 has reduced compressibility as compared
with the gasket 14. In an embodiment, the insulator layer 40 may
include a plurality of insulator films.
[0017] Information regarding the expected swelling of the catalyst
coated membrane 12m in solution can be gathered beforehand. Given
the expected membrane swell, compensation for the swell is made by
setting a thickness of the insulator layer 40 based on, or
corresponding to, a thickness of the swollen catalyst coated
membrane 12m. The thickness of the insulator layer 40 can also take
into account a desired gas diffusion layer G compression for smooth
mass transport and low contact resistance. In such manner, the
insulator layer 40 serves as a hard-stop to avoid over-compression
of gas diffusion layers G. Nafion 115 and a hydrocarbon membrane
were analyzed and tabulated. The values relating to membrane
swelling in x, y, and z direction at 1M and 8M methanol, 80.degree.
C. is given below in table 1.
TABLE-US-00001 TABLE 1 Nafion 115 Hydrocarbon membrane z x y z x y
1M MeOH 19 17 21 4 7 9 1M MeOH 31 23 31 31 13 14
[0018] When assembling a fuel cell stack, the stack is initially
compressed at a relatively low load based on the thickness of the
insulator layer 40. At this point, the catalyst coated membrane 12m
is substantially dry. Once the stack is assembled, a methanolic
solution flows into the anode 12a side, while maintaining the stack
within a desired temperature range. The catalyst coated membrane
12m swells and pushes against the gas diffusion layer G, thereby
compressing the gas diffusion layer G in-situ. The gas diffusion
layer G, upon being pushed by the swollen catalyst coated membrane
12m, contacts a plurality lands/ribs L provided on the flow field
plate 13a.
[0019] Further, as there is adequate free volume provided by the
insulator layer 40, there is reduced channel intrusion of the gas
diffusion layer G as a result of membrane swell. The stack is
thereafter compressed to a final load in one or more subsequent
compression operations. As catalyst coated membrane 12m is already
swollen, and a thickness of the compressed gas diffusion layers G
is therefore set, subsequent compression operations reduce the
contact resistance, while creating little or no mass transport
restrictions in the channel areas C. The effect of the insulator
layer 40 on membrane swell is illustrated in FIG. 5.
Advantageously, step-wise compression operations such as 750, 1000
Lb, 1250 in combination with the insulator layer 40, also serve to
desensitize the stack to variations in compressibility and
thickness of the gasket.
[0020] The foregoing description of the specific embodiments will
so fully reveal the general nature of the embodiments herein that
others can, by applying current knowledge, readily modify and/or
adapt for various applications such specific embodiments without
departing from the generic concept, and, therefore, such
adaptations and modifications should and are intended to be
comprehended within the meaning and range of equivalents of the
disclosed embodiments. It is to be understood that the phraseology
or terminology employed herein is for the purpose of description
and not of limitation. Therefore, while the embodiments herein have
been described in terms of preferred embodiments, those skilled in
the art will recognize that the embodiments herein can be practiced
with modification within the spirit and scope of the claims as
described herein.
* * * * *